1. Field of the Invention
The present invention relates to a transporting apparatus and method. The present invention is suitable for a transport mechanism of a pinless printer transporting continuous paper having no feed pins (or tractor pins). The continuous paper here falls into two categories: paper folded back at perforations formed per given length, and a continuous roll of paper.
2. Description of Related Art
Conventional continuous paper is formed with sprocket holes serving as through holes at side edges provided separably from a main body used as a printable area. The continuous paper is transported while feed pins of a paper transport system of a printer are engaging in the sprocket holes. Although such continuous paper has the advantage of being transported in a transport direction without being skewed or becoming slack, it takes processing costs to form through holes at both side edges. Furthermore, since the both side edges are unusable for printing, they must be separated at the termination of printing, leaving dust behind. For this reason, there are demands for the use of continuous paper having no holes at the both side edges. In this case, however, technologies are required for transporting the continuous paper in the transport direction without being skewed or becoming slack.
In a transport mechanism disclosed by Japanese Translation of Unexamined PCT Appln. No. 507666/1997, a paper position regulation unit is provided that presses one edge of holeless continuous paper against a stopper to regulate the position of the continuous paper with respect to a direction orthogonal to a transport direction, and a tension increasing unit and an accumulator are disposed at the following stage of the paper position regulation unit with respect to the transport direction (forward direction). The tension increasing unit, which is made up of a vacuum brake, increases tension on the paper to prevent swing or paper skew in the direction orthogonal to the transport direction of the paper. The accumulator, which is made up of a roller moving vertically, increases tension on the paper to remove slack in the paper in a back feed operation for transporting the paper in a direction opposite to the transport direction (forward direction) during printing. The paper is transported in the forward direction and the backward direction by a drive roller provided at the following stage of the accumulator with respect to the transport direction.
Since printers have been sped up, paper overruns several inches when it stops, and the paper must be run preparatorily several inches when printing is started. Accordingly, when printing is stopped and restarted, a back feed is performed to pull back the paper in the backward direction by the sum of the distances of the overrun and the preparatory run, thereby preventing an excessive space between an image printed previously and the next image to be printed. To stabilize the run of the high-speed printers during paper activation, a back feed amount must be increased to drop activation acceleration. This is because a high activation acceleration leaves inertia in a motor for driving a following drive roller and disables quick transition to a constant speed.
The above-described patent application has several problems. Specifically, (1) the separate arrangement of the tension increasing unit and the accumulator increases the size and cost of the transport mechanism. (2) Since the accumulator removes slack in the paper by vertical movement of the roller, large slack in the paper would increase the distance of vertical movement of the accumulator. Accordingly, if a back feed amount is increased to cope with the speedup of printers, a space for the vertical movement of the accumulator must be allocated in the apparatus, increasing the size of the apparatus. (3) Since vertical movement of the accumulator causes vertical changes in the transport direction, the paper is easily skewed and runs unstably. (4) The vacuum brake is susceptible to wear. Since the vacuum brake applies brake force in accordance with the width of the paper, a different brake force is applied for a different paper width. Therefore, for different paper types, the vacuum brake cannot always apply desired brake forces. (5) Since the tension increasing unit is disposed at the following stage of the paper position regulation unit with respect to the transport direction, paper slack occurring between the paper position regulation unit and the tension increasing unit cannot be removed. (6) Since the tension increasing unit must press a paper edge against the stopper so as not to crush (buckle) it, it is difficult to adjust press forces. Paper buckling limitations limit the types of usable paper. In other words, such a tension increasing mechanism is unsuitable for treating thin paper.